Multiple spawning events promote increased larval dispersal of a predatory fish in a western boundary current

Abstract

Transport of larvae by ocean currents is an important dispersal mechanism for many species. The timing and location of spawning can have a large influence on settlement location. Shifts in the known spawning habitat of fish, whether due to climate or the discovery of new spawning stock, can influence the distribution of juveniles and our understanding of connectivity. The globally distributed species; Pomatomus saltatrix, is one such example where a previously unrecognised summer spawning event and a more southern latitudinal extent was recently reported for the southwest Pacific population. Although restrictions are in place to protect the traditional spawning event, the importance of the newly recognised summer spawning event is uncertain. Here, we investigate larval dispersal of P. saltatrix using particle tracking simulations to identify the contributions of the different spawning events to settlement. By modelling dispersal of larvae released in northern and mid‐latitude regions over the Austral spring and summer, we show that the newly recognised mid‐latitude summer spawning event contributes over 50% of the larvae reaching southern latitudes. This is due to a reduced (1–2 days) pelagic larval duration (associated with temperature), resulting in reduced larval mortality, and the seasonal (summer) strengthening of the East Australian Current (EAC) transporting particles ~50 km further south. These findings demonstrate that in dynamic boundary current systems such as the EAC, the final settlement location of larvae that are transported by ocean currents can vary considerably depending on the timing and location of spawning and that multiple spawning events are important for maximum dispersal.

Coastal winds and larval fish abundance indicate a recruitment mechanism for southeast Australian estuarine fisheries

“…This aligns with previous research demonstrating rapid changes in larval fish transport and retention due to upwelling and downwelling for larvae of multiple taxa in various locations (Natunewicz et al , 2001; Ings et al , 2008). The consistently positive effect of downwelling favourable winds regardless of lag time supports our hypothesis that onshore transport may increase recruitment into estuaries by larval fishes is likely as they are geographically closer and stochastic dispersal will be reduced (Bruno et al , 2018; Schilling et al , 2020).…”

“…Our study used correlative analyses and several potential explanatory variables were not included in our models, which may have captured additional variance in either larval fish abundance or commercial fisheries catch rates. These include water temperature, oceanographic currents, larval swimming ability, varying population spawning biomasses or the effects of density dependence, all of which influence spawning and/or recruitment (Ottersen and Sundby, 1995; Schilling et al , 2020). The present study also did not investigate the abundance of larval fish entering estuaries, which would be an important metric to confirm increased recruitment following favourable wind conditions.…”

“…The present study uses data from the southeast Australian region (Figure 1), dominated by the East Australian Current (EAC). The EAC generally transports larvae poleward and adjacent to coastal and estuarine areas, which are juvenile nursery and rearing habitats (Roughan et al , 2011; Schilling et al , 2020). Together with the EAC, onshore winds are an important driver of upwelling and downwelling through Ekman transport mechanisms (Schaeffer et al , 2013, 2014).…”

Artificial reefs increase fish abundance in habitat‐limited estuaries

“…This study is based on the assumption that during our study, larval supply to estuaries was not a limiting factor for recruitment of juvenile fish. This larval supply is driven by the East Australian Current which consistently transports larvae poleward, distributing coastally spawned larvae to temperature estuaries along the east Australian coastline (Roughan, Macdonald, Baird, & Glasby, 2011; Schilling et al., 2020). For each sample period (year), samples from each reef site were taken on six randomly selected days over the same 3‐month season as the initial reef deployment (Table 1).…”

The Rate of Coastal Temperature Rise Adjacent to a Warming Western Boundary Current is Nonuniform with Latitude

“…Also shown are the correlations between the moored temperature data and satellite SST, the moored temperature trend at each location the time period 2010-2017, which is common to both the satellite SST and the moored observations, and the satellite SST trend for that same time period. Schilling et al, 2020). The domain extends from 25.3°S to 38.5°S, and from the coast to ∼1,000 km offshore.…”